The 60% rate of vaginal delivery achieved in the group for which it was planned was a big departure from the roughly 75% delivered surgically in usual clinical practice, noted Sarah Kilpatrick, MD, PhD, chair of obstetrics and gynecology at Cedars-Sinai in Los Angeles.

The study didn't consider other known advantages of vaginal delivery, such as faster recovery time, lower risk of multiple surgeries for the mother, shorter hospital stay, she pointed out in an interview.

"Cesarean section is a major surgery, and anything we can do to avoid those surgeries safely is important," she told MedPage Today. "This study adds to the indications for safe vaginal delivery in a specific population."

But practical considerations may mean that the results won't really change practice from what it has been, which has relied largely on observational studies, Michael F. Greene, MD, of Massachusetts General Hospital in Boston, suggested in an accompanying editorial.

"Given the trends in patient demographic characteristics and preferences, the virtual disappearance of vaginal delivery in cases of breech presentation, and the dramatic reduction in instrumented vaginal delivery (and the associated gradual disappearance of the skills necessary to perform these procedures among obstetricians), it seems unlikely that we will see a major change in use of cesarean delivery for twins nationwide," he wrote.

The Twin Birth Study only included qualified obstetricians experienced in vaginal twin delivery and centers that met standards for rapid emergency cesarean delivery.

Twins had to be alive, in the 1,500 to 4,000 g weight range, and with the first twin pointed head first.

The results can't be generalized to other circumstances, Kilpatrick pointed out.

The trial included 2,804 women at 106 centers in 25 countries randomized at 32 to less than 39 weeks' gestation to planned C-section or planned vaginal delivery with induction of labor at 37 to less than 39 weeks' gestation.

Planned vaginal delivery group was reassessed at the time of labor and 40% of cases shifted to medically-indicated cesarean for both twins (30% during labor) and 4% for one twin only.

In the planned cesarean group, 89% had a cesarean delivery for both twins whereas 9% delivered vaginally for both.

Planned vaginal delivery gave the twins a little extra gestation time as well, with a mean of 13.3 versus 12.4 days from randomization to delivery (P=0.04) and a slightly older gestational age at delivery as well (P=0.01).

While the incidence of the composite primary outcome differed among gestational age groups, planned route of delivery didn't make an apparent difference in any of those groups.

Maternal death or serious maternal morbidity before 28 days postpartum came out similar between planned cesarean and planned vaginal delivery, with rates of 7.3% and 8.5%, respectively (P=0.29).

The researchers cautioned that the study wasn't powered for subgroup analysis, so further study may be warranted for the small group of infants born at 37 to 38 weeks' gestation.

They pointed out that the 95% confidence intervals for the primary outcome were consistent with no more than a 23% reduction and no more than a 74% increase in the odds of fetal or neonatal death or serious neonatal morbidity with planned cesarean versus planned vaginal delivery.

The study was supported by a grant from the Canadian Institutes of Health Research.

The researchers reported having no conflicts of interest to disclose.

Greene reported that he is an associate editor at the NEJM.

Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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